This flag causes the shairport-sync server to attempt to daemonize, but it looks like systemd is already handling that. With the `-d` argument, shairport-sync immediately exits—it seems that something (systemd I'm guessing?) is sending it SIGINT or SIGTERM.
The [upstream systemd unit](https://github.com/mikebrady/shairport-sync/blob/master/scripts/shairport-sync.service.in#L10) doesn't pass `-d`.
The shairport-sync service currently fails to start with the error
shairport avahi_entry_group_new failed
This problem seems to have been introduced by
cdd7310a50
After some trial and error I concluded that the attached commit is a minimal
fix.
Adds a new service module for shairport-sync. Tested with a local
and remote pulseaudio server. Needs to be run as a user in the pulse group
to access pulseaudio.
